This research project attempts the isolation, description, and functional analysis of secondary color coding systems (i.e., color processing beyond the level of primary retinal receptors) in relation to the perception of form (grid patterns). The project utilizes the McCollough Effect, a color orientation specific aftereffect, as well as other color contingent aftereffects, which are felt to result from color coding in post-retinal color centers. The current research will involve the measurement via a projection colorimeter of perceived aftereffect colors which have been established by narrow-band interference filters throughout the visible spectrum. By observing the shift in perceived color matches as a function of the spectral components of the adapting patterns, it is hoped that the peak sensitivities of these units can be established. Further, by selectively adapting the retinal receptors prior to the presentation of the McCollough inspection patterns, estimates of the range of sensitivity (color coding) of secondary color units can be made.